The present invention relates to a wire cut electric discharge machining apparatus for machining a workpiece which is placed in a machining solution contained in a machining reservoir, and more particularly to a sealing structure for the machining solution, which is capable of preventing leakage of the machining solution during machining.
With such a wire cut discharge machining apparatus, a workpiece in a machining solution is machined by a wire electrode which is movable in X and Y directions relative to a machining reservoir. An arm for supporting the wire electrode is adapted to penetrate a side wall of the machining reservoir, so that the arm is allowed to project into the machining reservoir.
FIG. 1 is a schematic diagram illustrating an example of a conventional sealing structure in a wire cut electric discharge machining apparatus. In FIG. 1, reference numeral 1 denotes a machining reservoir; 2, a machining solution; 3, an arm passing through the side wall of the machining reservoir 1 which is movable in X and Y directions relative to the machining reservoir 1; 1a, a through window elongated in a horizontal direction and provided at the side wall of the machining reservoir 1 to allow the arm 3 and the machining reservoir 1 to move relative to each other in a direction, for example a Y direction; 4, a steel seal installed in the through window 1a; 5, a seal receiver to which the steel seal 4 is fixedly secured; 5a, a through hole formed to the seal receiver 5 so as to allow the arm 3 move in the other direction, for example an X direction, relative to the machining reservoir 1; and 6, a pipe seal for preventing the machining solution 2 from leaking through a gap between the arm 3 and the seal receiver 5. A supporting member 1c is provided along a circumference of the through window 1a to retain the steel seal 4 within a slight gap 1b formed between the supporting member 1c and the side wall of the machining reservoir 1. The steel seal is provided to minimize amount of leaked machining solution 2.
In such a conventional wire cut electric discharge machining apparatus, the steel seal 4 is urged toward the supporting member 1c in the X direction shown in FIG. 1 due to a hydraulic pressure of the machining solution 2. This results in an occurrence of a strong contacting pressure between the steel seal 4 and the supporting member 1c. Consequently, when the arm 3 moves in the Y direction relative to the machining reservoir 1, the steel seal 4 slides along the supporting member 1c with a large frictional resistance.
The arm 3 also slides in the X direction through the hole 5a with a frictional resistance between the pipe seal 6 and the arm 3. If the frictional resistance therebetween is relatively large, the resistance in the X direction causes a deformation of the arm 3 in the Y direction whereby displacement of a wire guide supported by the arm 3 is caused. As a result, it is disadvantageous that the machining accuracy may be degraded and further the frictional resistance between the pipe seal 6 and the arm 3 in the X direction may cause the steel seal 4 to be damaged.